1. Field of the Invention
This invention relates to a process of manufacturing a sliding surface bearing comprising a backing shell of steel, a bearing metal layer on the backing shell, and a copper-containing sliding surface layer, which has been electrodeposited over the bearing metal layer, wherein the backing shell is provided throughout its rear surface, which constitutes the rear surface of the bearing, with a tin-containing corrosion-resisting layer after the sliding surface layer has been deposited.
2. Description of the Prior Art
To deposit the sliding surface layer over the bearing metal layer, which usually consists of a copper or aluminium alloy, a plurality of backing shells to which the bearing metal layer has been applied by casting or cladding are axially clamped together and immersed in a suitable electrodeposited bath. In general, the sliding surface layer is not directly deposited on the bearing metal layer but is electrodeposited on an intermediate layer, which consists of nickel or a nickel alloy and serves as a diffusion barrier or a primer. Whereas the backing shells are so arranged in the electrodeposition bath that the sliding surface layer can be electrodeposited only on the bearing metal layer or on the intermediate layer, the fact that the copper which is dissolved in the electrolyte from which the sliding surface layer is electrodeposited has a higher electric potential than the iron of the backing shell will result in a deposition of copper metal on the rear surface of the backing shell. For this reason a layer of tin or a tin alloy must be deposited on said copper layer to protect the rear surface of the bearing from corrosion. In that case diffusion processes will result particularly under the action of heat in the formation of a brittle copper-tin phase, which owing to the changes of volume will give rise to internal stresses in the multilayer composite thus formed. Because owing to the cementation of the copper the adhesion between the copper layer and the backing shell of steel is relatively low, the internal stresses may cause the corrosion-resisting layer and the copper layer to spall in part. The continual micromotion of the backing shells relative to the support on which the backing shells are held by an inteference fit will cause the detached material to migrate away under the conditions of the interference fit so that material comprising the detached material, the inevitably abraded iron, and oil coke will accumulate in certain regions on the rear surface or the backing shell. Such accumulated material will disturb a uniform distribution of load so that the wear of the sliding surface layer will be increased and the sliding surface layer may suffer fatigue fractures in those regions.
In sliding surface bearings comprising an aluminium-base bearing metal layer and a sliding surface layer consisting of a zinc-phosphate alloy it is desired to avoid a deposition of a zinc-phosphate layer on the rear surface of the backing shell of steel during the electrodeposition of the sliding surface layer. To that end it is known from Published German Patent Application 37 27 468 to coat the backing shell on its rear surface with a layer which will prevent a deposition of a zinc-phosphate layer and which before the deposition of the sliding surface layer is removed from the surface on which the sliding surface layer is to be deposited. It is proposed to make such protecting layers from various materials, such as tin, copper, lead, nickel, and chromium. But the proposal to prevent by the provision of a protecting layer the undesired formation of a metal layer on the rear surface of the bearing cannot be adopted to prevent a cementation of copper because economically satisfactory protecting layers For that purpose are not known.